Conventionally, piezoelectric materials have been used for ultrasonic wave motors, piezoelectric transformers, sounding bodies, actuators, sensors, and the like. For such applications, studies on the composition and the microstructure have been made for property improvement of the piezoelectric material. In addition, by the property improvement, miniaturization of the apparatuses and the elements, improvement in the energy conversion efficiency, and the like have been made.
As the piezoelectric material, there are used various materials containing so-called PZT (lead zirconate titanate) as the main component (hereinbelow referred to as a PZT based piezoelectric material). In an application for the use of resonance as in an ultrasonic wave motor or a piezoelectric transformer, it has been known that a material having a larger mechanical quality factor (Qm) is preferable because of a larger resonance displacement and little heat generation. Therefore, regarding the PZT based piezoelectric material, property improvement for raising the Qm by adding Mn or Co is tried.
In addition, it has been known that a PZT based piezoelectric material requires high temperature of about 1250° C. for firing and that Pb evaporates from about 1000° C. during the firing. When such evaporation of Pb from the piezoelectric body is caused, in a piezoelectric body obtained after the firing, there may be caused a problem of deterioration in piezoelectric properties, specifically, electromechanical coupling coefficient, relative permittivity, mechanical quality factor, or elastic compliance due to composition deviation caused by insufficient Pb or a problem of property deviation. In addition, when firing of about 1250° C. is required, an electrode material which can withstand the firing at the temperature is required for the electrode layer formed between the piezoelectric layers. Therefore, expensive platinum or an electrode material containing platinum as the main component is used, which is a factor of high cost of a piezoelectric element.
The aforementioned problems are unexceptional also with regard to an ultrasonic wave motor where a plurality of layers of piezoelectric material and electrode material are laminated. For example, the ultrasonic wave motor disclosed in Non-Patent Document 1 is a motor element using a primary vertical-secondary flexing mode and relating to a piezoelectric motor element where rectangular piezoelectric layers and electrode layers formed to divide the piezoelectric layers into two almost equally are alternately laminated. This ultrasonic wave motor also has a problem of reduction in resonance displacement because of large temperature rise of the element when it is used with a resonance frequency.
For this problem, development of a piezoelectric material having a large mechanical quality factor has been addressed. The mechanical quality factor (Qm) is the reciprocal of the coefficient of mechanical loss (tan δm), and a large Qm means a small tan δ. When tan δ is large, heat generation upon resonance is large, and, when the element temperature rises due to the heat generation, element properties are deteriorated. Therefore, increase in mechanical quality factor has been tried.
In addition, in the case of a Pb based piezoelectric body containing Mn, Mn often has a composition which is for being added to a complex perovskite oxide having a stoichiometric composition as shown in Patent Document 1. That is, the material design is to allow Mn to be present as a phase different from the complex perovskite oxide.
[Patent Document 1] JP-A-2002-338349
[Non-Patent Document 1] Actuator 2006 Proceeding Al. 1 (Piezoelectric Ultrasonic Motors for Lens Positioning of Cellular Phone Camera Modules)
However, it is general that the mechanical quality factor is evaluated by a measurement value in a low electric field of about 1 V/mm set in the former Japan Electronic Materials Industry Association Standard (EMAS), and the evaluation was in a low electric field in comparison with an electric field used as a piezoelectric element. As a result of detailed studies in this respect, it became clear that the mechanical quality factor measured in a high electric field of, for example, 10 V/mm is small in comparison with the value in a field of 1 V/mm. In addition, it became clear that the change in the Qm value by the electric field differs depending on the material.
Therefore, when an element is manufactured with a material having a large decrease of Qm in a high electric field with respect to Qm in a low electric field, even if the resonance displacement is tried to be increased by, for example, increasing the electric field, it is impossible to obtain resonance displacement as much as expected.
In addition, in the case that a Pb based piezoelectric body contains Mn, it was found that, actually, Mn is taken into a B site of the perovskite structure in a step of firing or the like to cause a loss of the A site component with respect to the B site component, or Mn is taken into the B site to make the B site excess to allow ZrO2 to deposit as a different phase as a result. In addition, both the case that the A site component has a loss and the case that ZrO2 deposits as a different phase had a problem of allowing the piezoelectric properties to deteriorate.